Update apollo/client and minor dependencies updates

[francescoparra]

Summary

Updates @apollo/client to v4 along with minor dependency updates.

Changes

• Upgrade @apollo/client to v4
• Update tests affected by the Apollo Client v4 upgrade
• Update minor dependencies
• Add a deprecation notice to the README

Notes

This keeps the addon up to date with the latest Apollo Client release while documenting its deprecation status.

[francescoparra]

@josemarluedke

The main purpose of this PR is to keep the dependency usable for now by updating it to work with the latest version of @apollo/client.

Since you previously suggested me to consider a switch to glimmer-apollo, I also thought it would make sense to add the deprecation notice here to make that direction clear to users.

That said, I'm happy to remove the deprecation if you think it's unnecessary or premature.